In order to keep the matriarchy safe, the Vuvalini would banish the boy-children to the outer swamps of The Green Place.
When boys reached puberty they would be visited by the Vuvalini only for sperm milking and the odd ritual of family.
Early reports from test screenings mentioned, however that there were scenes of the Crow Fishers seen hunting for crows with help of kites and fishing nets, so there definitely are more scenes filmed with them.
According to production designer - Colin Gibson, the Crow Fishers are a remnant of the Vuvalini system.
If you look at studies now you'll see that women have an average 9 year age range either side of their own with a preference for a small 4 years either side of their own age.
Men may not like this trend but it's happening with or without their approval.
So maybe there is a kernel of truth the rule, at least for men. Le's research focuses on commitment, including the factors associated with commitment and its role in promoting maintenance.